Fluorine magnetic resonance studies of fluorine-substituted benzoyl chymotrypsins

The fluorine magnetic resonance spectra of 4-fluorobenzoyl and 3,5-di(trifluoromethyl)benzoyl-alpha-chymotrypsins and the corresponding methyl esters were determined. An unusually large downfield displacement of the chemical shift (-10 ppm) was observed for the 4-fluorobenzoyl-alpha-chymotrypsin compared to the free acid in water. The shift of the ethyl ester was displaced upfield on going from a partly aqueous solvent to dioxane or methanol. The line broadening of the fluorine resonance of the 3,5-di(trifluoromethyl)benzoyl-alpha-chymotrypsin was minimal and there was no evidence of two peaks in the spectrum. The resonance was displaced only slightly downfield from the corresponding acid in water. Unusual chemical shifts for fluorinated acylchymotrypsins have been reported for other acyl groups and they appear to be unrelated to the anomalous deacylation rates observed for some fluorine substituted acylenzymes.